Duplicate mac-addresses on CAT 6513 - Is this a problem?

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Jan 13th, 2010
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6513-#sh mac-address-table address 0007.b32b.d2c0
Legend: * - primary entry
        age - seconds since last seen
        n/a - not available

  vlan   mac address     type    learn     age              ports
------+----------------+--------+-----+----------+--------------------------
Supervisor:
*  110  0007.b32b.d2c0    static  No           -   Router
*  100  0007.b32b.d2c0    static  No           -   Router
*  210  0007.b32b.d2c0    static  No           -   Router
*  220  0007.b32b.d2c0    static  No           -   Router
*  200  0007.b32b.d2c0    static  No           -   Router
*  230  0007.b32b.d2c0    static  No           -   Router
*  460  0007.b32b.d2c0    static  No           -   Router
*  496  0007.b32b.d2c0    static  No           -   Router
*  495  0007.b32b.d2c0    static  No           -   Router
*  330  0007.b32b.d2c0    static  No           -   Router
*  320  0007.b32b.d2c0    static  No           -   Router
*  340  0007.b32b.d2c0    static  No           -   Router
*  350  0007.b32b.d2c0    static  No           -   Router
*  380  0007.b32b.d2c0    static  No           -   Router
*  360  0007.b32b.d2c0    static  No           -   Router
*  ---  0007.b32b.d2c0    static  No           -   Router
*   50  0007.b32b.d2c0    static  No           -   Router
*    7  0007.b32b.d2c0    static  No           -   Router
*    1  0007.b32b.d2c0    static  No           -   Router
*    9  0007.b32b.d2c0    static  No           -   Router
*  190  0007.b32b.d2c0    static  No           -   Router
*  180  0007.b32b.d2c0    static  No           -   Router
*  420  0007.b32b.d2c0    static  No           -   Router
*  390  0007.b32b.d2c0    static  No           -   Router
*  310  0007.b32b.d2c0    static  No           -   Router
*  300  0007.b32b.d2c0    static  No           -   Router
*  280  0007.b32b.d2c0    static  No           -   Router
=================================================
The above MAC addresses are the BIA ( Burnt in addresses of many ports in this CAT 6513 ) and can also be seen when doing show interface command as follows:
Partial Output:
==========
Vlan7 is up, line protocol is up
  Hardware is EtherSVI, address is 0007.b32b.d2c0 (bia 0007.b32b.d2c0)
  Description: GCAOA 2 NAL - Link 1
  Internet address is 10.120.253.225/29
  MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,
     reliability 255/255, txload 2/255, rxload 2/255
  Encapsulation ARPA, loopback not set
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:02, output 00:00:00, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/278/278 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 9307000 bits/sec, 1767 packets/sec
  5 minute output rate 8782000 bits/sec, 1780 packets/sec
  L2 Switched: ucast: 362482 pkt, 32307959 bytes - mcast: 956576 pkt, 85398380 bytes
  L3 in Switched: ucast: 1867504285 pkt, 1443931102771 bytes - mcast: 0 pkt, 0 bytes mcast
  L3 out Switched: ucast: 1815701229 pkt, 961832705341 bytes mcast: 0 pkt, 0 bytes
     1868623791 packets input, 1444029196575 bytes, 0 no buffer
     Received 757142 broadcasts (757142 IP multicast)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     1816765552 packets output, 961914556799 bytes, 0 underruns
     0 output errors, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out
Vlan9 is up, line protocol is up
  Hardware is EtherSVI, address is 0007.b32b.d2c0 (bia 0007.b32b.d2c0)
  Description: Communications - GWAN
  Internet address is 10.120.253.251/28
  MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,
     reliability 255/255, txload 2/255, rxload 2/255
  Encapsulation ARPA, loopback not set
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input 00:00:00, output 00:00:00, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/1/1 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 10929000 bits/sec, 2124 packets/sec
  5 minute output rate 10061000 bits/sec, 2228 packets/sec
  L2 Switched: ucast: 12295147 pkt, 1330274178 bytes - mcast: 6861848 pkt, 506128599 bytes
  L3 in Switched: ucast: 2198266998 pkt, 1224275689345 bytes - mcast: 0 pkt, 0 bytes mcast
  L3 out Switched: ucast: 2552911947 pkt, 1847139656199 bytes mcast: 0 pkt, 0 bytes
     2214829509 packets input, 1225864174517 bytes, 0 no buffer
     Received 6861858 broadcasts (2358354 IP multicast)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     2565064604 packets output, 1848442726830 bytes, 0 underruns
     0 output errors, 0 interface resets
     0 output buffer failures, 0 output buffers swapped out
Vlan10 is administratively down, line protocol is down
  Hardware is EtherSVI, address is 0007.b32b.d2c0 (bia 0007.b32b.d2c0)
  Description: Management Vlan (not in production yet)
  MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input never, output never, output hang never
  Last clearing of "show interface" counters never
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     0 packets input, 0 bytes, 0 no buffer
     Received 0 broadcasts (0 IP multicast)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 packets output, 0 bytes, 0 underruns
     0 output errors, 1 interface resets
     0 output buffer failures, 0 output buffers swapped out
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ohassairi Wed, 01/13/2010 - 21:16
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this is normal and expected

astanislaus Wed, 01/13/2010 - 21:33
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I thought so. But can this be explained with a reason which is what the customer is asking.

Giuseppe Larosa Thu, 01/14/2010 - 00:18
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Hello Alphonse,

the choice in Cisco multilayer switches is to use the same MAC address for all SVI interfaces


0007.b32b.d2c0


this is not a problem because CAM tables use Vlan, MAC address, port so it does not create ambiguities.

The device has a block of MAC addresses that can be seen with sh module but it uses only one.

The same happens for STP with extended system-id option.


In each Vlan an ARP request for SVI IP address will get the answer 0007.b32b.d2c0


There are specific cases when you need to assign a different MAC address to an SVI and this can be done with mac-address command like in this example:

router#sh run int vlan 617


Building configuration...


Current configuration : 355 bytes
!
interface Vlan617
description xxxx
mac-address 000e.847e.87c2
mtu 1520
ip address 10.82.8.98 255.255.255.240
ip pim dr-priority 10
ip pim sparse-mode



Edit:

Ganesh in another thread has found a link that explains support of same MAC address on multiple SVIs that can help


http://www.cisco.com/en/US/products/hw/switches/ps700/products_tech_note09186a00801c9b4e.shtml



Hope to help

Giuseppe

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